DE69526932T2 - COMMUNICATION VIA A SERIAL LINE - Google Patents

Abstract

The present invention pertains to a method and a system for synchronization of time slots to a part of an a.c. net frequency half cycle as well as an apparatus for performing the synchronization. More particularly it relates to a transfer method and a system for communication of pulse signals over a series cable powered by a constant current regulator for control and monitoring of lightings, lamps, sensors, detectors and other loads. It specifically relates to the technical field of control and monitoring of airfield lighting systems (TWY1, TWY2, TWY3, SB1, LO1) including sensors for Surface Movement and Guidance Control Systems (SMGCS).

Description

Field of the invention

The present invention relates to a message transfer method and system for controlling and monitoring lights, lamps, sensors, detectors and other loads, and in particular for controlling and monitoring airfield lighting systems with surface motion and guidance control system (SMGCS) sensors.

History of the state of the art

The lamps for airport lighting systems are most often powered by a constant current power supply via a serial cable. Such lamps are connected in series with the supply cable using isolation transformers. A common type of automatic lamp monitoring system monitors the current and voltage supplied to the serial cable. If a lamp fails, the impedance in a loop of lamps changes and this is reflected in the current and voltage supplied. A disadvantage with this method is that there is no information as to which lamp has failed. Thus, it is difficult to determine the urgency of replacing the lamp. Furthermore, if a large number of lamps are fitted in the loop circuit, the change in impedance due to the lamp failure may be so small that it is difficult to detect. If several lamps fail, the change in impedance becomes larger.

Another type of monitoring system is based on assigning a unique address together with a monitoring unit to each lamp. If the lamp fails, the unit short-circuits the lamp and periodically breaks the short-circuit in a timed sequence determined by the lamp's address. Identifying the failed lamp is done by determining the time (with respect to some reference) related to the measurements of the disturbances in voltage or current via a detector connected to the primary side of the series transformers. Again, the change in impedance due to a lamp failure may be so small that it is difficult to detect, but this time the short-circuit is released for each lamp, one at a time, so that only one lamp at a time signals a failure to a main monitoring unit.

Such prior art systems are known from US Patent No. 5,359,325 to Ford et al., European Patent No. 0 445 773 to Taniguchi et al. and European Patent No. 0 448 358 to Watanabe. These systems rely on the saturation of series isolation transformers. An isolation transformer of the type used in airport lighting systems saturates, i.e. acts like an air coil with almost no impedance, when a lamp failure occurs on the secondary side of the transformer, thereby creating disturbances on the primary side due to the flux change. The flux change is detectable, but in some cases it is difficult to distinguish it from other disturbances, such as those caused by mains frequency current zero crossings when the current is thyristor modulated, which is common practice. It is particularly difficult to detect disturbances due to flux changes when a batch of transformers is connected in series.

Furthermore, these documents do not teach communication during a short portion of a power frequency half cycle (a power frequency half period). Signals in the cited documents are transferred over much longer periods of time without regard to zero crossings. The inventions according to the above cited documents affect the impedance, but without taking into account whether the impedance switches between a high and low value during a power frequency half cycle.

Another prior art document, disclosed by US Patent No. 4,398,178 to Russ et al., teaches a system for transmitting information on an AC power line. This cited document has certain distinguishing features, and at least two lines are connected to an AC power supply. Another feature relates to amplitude reductions produced by means of a normally shorted impedance.

Furthermore, document US Patent No. 4,398,178 shows a method for transmitting pulse signals from the power generator side to a number of receivers. The receivers respond according to a method that cannot be implemented in an airfield lighting system with communication via a serial cable. It assumes a separate power transformer that is used only for communication, since it is normally short-circuited. The transmitting unit communicates via interruptions of a short-circuited transformer (impedance). In addition, its receiving units communicate via a load and not via a Transformer. Accordingly, the disclosed system communicates with different devices for uplink and downlink communication:

From US-A-4,024,528 a remote switching system is known with the objective of improved remote switching using an AC power line. The system uses the relatively quiet or noise-free part of the first half cycles of the AC line voltage to transmit and switch control signals.

Summary of the disclosed invention

The cited documents US patent No. 5,359,325, European patent No. 0 445 773 and European patent No. 0 448 358 do not teach communication during a short part of a mains frequency half cycle, which is essential for the operation of the present invention. The present invention generates a voltage pulse during a short time of the mains frequency half cycle. The totality of the pulses so generated during a specific half cycle are transmitted as a pulse signal on the serial cable. This is not disclosed in the documents, where signals are transmitted during much longer periods of time without considering zero crossings. The inventions according to the latter documents also affect the impedance, but without considering whether the impedance switches between a high or low value during a mains frequency half cycle. The present invention always involves the use of a controlled high impedance for communicating pulses contained in pulse signals.

The aforementioned US Patent No. 4,398,178 teaches a system for transmitting information on an AC power line. This document contains features that differ from the present invention. It has at least two conductors connected to an AC power source, and in the present invention only one conductor is connected. Another difference to be noted is that amplitude reductions are produced by means of a normally shorted impedance, in contrast to the present invention which does not communicate in any way with a shorted impedance, but communicates through short interruptions via a switch connected in series with the load.

Furthermore, US Patent No. 4,398,178 discloses a method for transmitting pulse signals from a power generator side to a number of receivers. The receivers respond according to a method which is Airport lighting system with communication on a serial cable is not implementable. It assumes a separate current transformer which is used only for communication as it is normally short-circuited. The transmitting unit communicates via interruptions of a short-circuited transformer (impedance), which is completely different from the present invention where transformers are only short-circuited during a lamp fault.

In addition, their receiver units communicate through a load and not through a transformer. Thus, the system disclosed in U.S. Patent No. 4,398,178 communicates with different devices for uplink and downlink communication. To implement a system as disclosed in U.S. Patent No. 4,398,178, for example in an airport system for monitoring airport lighting, a complete redesign of an existing system would be required.

The present invention can be easily applied to an existing system. Existing current transformers are used to supply a load and to generate high frequency pulse signals, where a pulse signal contains a number of pulses and where each individual pulse is generated by pulsing the impedance for a short time (generating a high impedance) compared to a half cycle in which current flows. The interruption of the secondary side circuit is thus so short that the influence on the energy supplied to a load is negligible.

The present invention relates generally to a system and method for message transfer between a main control system and addressable monitoring switches for a lighting system. Such switches are connected in series to the supply cable using isolation transformers and on the other hand they are attached to a load which they monitor. Examples of such loads could be lamps and sensors. A sensor could for example be of a magnetic, inductive, optical etc. type for detecting or measuring the presence of obstacles, for example vehicles.

To overcome the above problems, a technical problem of the present invention is to provide a method for synchronizing a time slot in each half cycle of the AC mains frequency such that harmonics that interfere with the relatively high frequencies used for message transmission are avoided. Mains frequency harmonics are common due to the fact that AC current is often controlled by thyristors, which almost certainly generate harmonics at zero crossings.

Another technical problem of the invention is to create a system with a message scheme with time slots for synchronized communication between affected units.

Another technical problem of the invention is to provide a communication system that can be easily integrated into an existing airfield lighting control system via small LMS and/or SIU modules attached to existing standard components, such as standard lighting transformers, sensors, lamps, cables, etc. A main control system is similarly attached to the series cable via a standard transformer.

An additional other technical problem of the invention is that the control and monitoring system is formed starting from the secondary side of the transformers, which represents a great advantage compared to systems provided on the primary side of a transformer.

An additional further technical problem of the invention is to provide a device for switching directly between a stationary sequence for monitoring LMS and/or SIU modules and a state where sequences are to be sent to the LMS and/or SIU modules from a main control unit.

The invention is defined by the appended claims.

Short description of the drawing

For a more complete understanding of the present invention and with regard to further technical problems and advantages thereof, reference is made to the following description taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a schematic block diagram layout of an existing prior art airfield lighting monitoring system with light monitoring switches (LMS) and a main control system;

Fig. 2-4 are schematic block diagrams for some of the blocks shown in Fig. 1;

Fig. 5a and 5b representations of a thyristor-modulated mains frequency curve and its high-pass filtered response, each with the fundamental frequency filtered out;

Fig. 6 is a scheme of square waves used to synchronize a time slot to the mains frequency, according to a preferred embodiment;

Fig. 7 shows a circuit used to generate the square waves according to Fig. 6;

Fig. 8 shows a series circuit with its connectors and interfaces according to the invention;

Fig. 9 shows an airport lighting system according to the present invention;

Fig. 10 the procedure for carrying out the exchange of information at a structural level;

Fig. 11 shows a setting sequence for the time slots according to the present invention; and

Fig. 12 a setting sequence for sending a command message.

Detailed description

Figures 1-5, in conjunction with the corresponding description, illustrate a prior art airfield lighting system according to the principles taught in conjunction with the co-pending international application published under WO/94/13119, assigned to the assignee of the present invention, entitled "Systems and methods for transmitting pulse signals" by Lars Millgard. The present invention has the capability of applying such a system to the implementation of its technical problems.

The airfield lighting monitoring system shown in Figure 1 includes a number of power supply loops 2 for lamps 4, and only one of the loops is shown in its entirety in the figure. Each lamp 4 is connected in its associated loop 2 via a secondary winding 5 of an isolation transformer 6, and the primary winding 8 thereof is connected in series in the power supply loop, and via a light monitoring switch (LMS) 10. Each power supply loop 2 is fed by a constant current regulator unit (CCR) 12 via a communication unit 14. A concentrator unit (CU) 16 is connected to a group 18 of the communication units 14 via a multipoint configuration. The units 14 and 16 are described more fully below.

The CU unit 16 and its associated elements, as described above, together form a sub-unit 20, which may, for example, be assigned to a may be assigned to a specific part of the lighting system of an aerodrome. The lighting system may include a required number of similar sub-units, some of which are designated 20' and 20".

The CU units 16 in the subunits are connected to a central concentrator unit 22 via multipoint modems.

The central CU unit 22 may be connected to a computer 24 with a display 25. The computer 24 may also be connected to other systems, for example via a local area network (LAN) 26. The unit 22 and the computer 24 may be located, for example, in a control room 27, or at any other suitable location.

Generally, for isolation transformers used in a system supplied with a constant current, the current flowing through the secondary winding is proportional to the current flowing through the primary winding and, under certain restrictions, independent of the load on the secondary side. The voltage across the primary winding is proportional to the voltage on the primary side. The proportionality in both cases is mainly due to the relationship between the number of turns of wire in the windings. A communication unit 14 detects responses from the LMS modules and reports the addresses of the non-responding modules to the central concentrator unit 22 via a local CU unit 16. In the central concentrator unit 22, the addresses are stored in a database accessible to the computer 24 in the control room 27.

The number of failed lamps 4 and the position of each failed lamp can be shown on the display 25. Different alarm criteria can be set in the central concentrator unit 22 via the computers 24.

As described in more detail below, communication between the LMS modules and the assigned communication unit takes place via high frequency signals that are superimposed on the 50 Hz or 60 Hz current in the power cable.

A schematic block diagram of an LMS module 10 is shown in Fig. 2, which also shows the connection of the lamp 4 to the circuit with the secondary winding 5 of the transformer 6.

The LMS module 10 is shown schematically as including a switch 30 connected in series with the lamp 4 for interrupting the current in the lamp circuit. The module 10 further includes a control circuit or logic unit 22, e.g. a microprocessor for controlling of the switch 30, an address memory 34 for storing the above-mentioned address thereof and a receiver 36 connected to receive the synchronization signal from the unit 14 and to forward it to the logic unit 32 of the module 10, and it also contains a DC power supply unit 38 for the logic unit 32 and the receiver 36.

A switch 42 is also connected across the secondary winding 5 and thus parallel to the lamp 4, which is controlled by the control circuit 32. In a manner known to those skilled in the art, the switch 30 can be based, for example, on the use of field effect transistors.

The memory for storing the address of each LMS module 10 can be a PROM memory.

A schematic block diagram of the communication unit 14 is shown in Fig. 3. The communication unit includes a series connection modem (SCM) 60, a series connection filter (SCF) 62 and a coupling transformer 6.

The SCM 60 is connected via the transformer 64 to the series circuit 2 for supplying the lamps 4, for sending the synchronization signals and for detecting the responses from the LMS modules. The SCM 60 is also connected to the concentrator 22 for reporting the address of the LMS modules with failed lamps.

The filter 62 reduces noise in the current coming from the CCR 12 and prevents signals coming from the SCM 60 and the modules 10 from being fed back into the regulation unit 12.

Referring to Fig. 4, the concentrator unit 16 includes a microprocessor 70, a modem 72 and a power supply 74. Connections to an information system, not shown, to the SCM units 14, to the computer 24 and to the power grid are designated 76, 78, 80 and 82, respectively.

The function of the CU unit 16 is to collect the information from the connected communication units 14 and to store it in a database of the microprocessor 10, where the computer 24 in the control room 27 can access it.

The CU unit 16 may also be designed to test the collected data against alarm criteria and, if necessary, issue an alarm.

With a monitoring and control system of the type described above, any lamp in airport lighting circuits can be individually. The system can provide continuously updated information on the location of failed lamps. A device can be arranged to display the information locally or to transmit it to any other information system at the airport.

The system does not require any extra cabling in the field, and it works with existing power cables.

The LMS module 10 can store its address in an EEPROM memory 34, which allows changing the stored address and receiving its address in a binary code.

In a preferred embodiment of the control and monitoring system of the present invention, use is made of a main controller, LMS and/or DIU modules connected to standard transformers on the secondary side thereof. The SIU module is a programmable and addressable microprocessor-based sensor interface module with almost the same function for the surface movement and guidance control sensors as an LMS module has for a lamp. It operates on the secondary side of an isolation transformer, meets the same environmental conditions as an isolation transformer, and it operates in the current range of 2.8 A to 6.6 A. A SIU module supplies a sensor 9 and monitors its output. A sensor output can be of the type presence detection, heading detection or operating point detection, sensor self-tests, etc. Generally, sensors used relate to surface movement and guidance control systems (SMGCS). As mentioned, the system transfers information between the main control system and the LMS units 10 in both directions, such as address and control information from the control system and status information from the LMS module, and the same applies to a SIU module.

Furthermore, the exchange of information takes place via signaling with high frequency signals, i.e. a high frequency relative to the mains frequencies, which are often 50 or 60 Hz frequencies, so that the information transfer is preferably carried out at frequencies of, for example, 4-7 kHz. This generally low frequency band is chosen due to some disadvantages of signaling with even higher frequencies in communication on serial cables, for example:

- High attenuation during signaling between the primary and secondary sides of the transformers;

- high attenuation of those lamp transformers that are attached to the cable loop;

- Generation of oscillation nodes in long series cables, and

- Crosstalk between different series cables.

One of the principles underlying the present invention relates to mains frequency synchronization to minimize mains-generated distortions and coding with minimal overhead using a small part for addressing purposes. The series circuits in an airport lighting system are generally fed by a CCR unit 12. Significantly, current control is often achieved by influencing their current waveform, for example via a thyristor control, see Figs. 5a and 5b, which show representations of a transistor-modeled mains frequency waveform and its high-pass filtered response with the fundamental frequency filtered out. Since the waveform of the current therefore deviates from a purely sinusoidal one, it contains the harmonics 84 that can occur in the frequency range used to carry out the communication. Harmonics 84 of the fundamental frequency mostly occur when the current control device - e.g. B., a transistor is turned on or off, e.g. at the zero crossings 86 of the curve associated with the modulated current. The LMS/SIU system according to the invention only generates a TS synchronization for information transfer at time intervals in each half-grid cycle where the content of harmonics and other distortions in the AC line frequency current is low.

A preferred embodiment of the present invention uses the transmission of "1" and "0", with one bit being sent at each half cycle of the mains frequency in a time slot TS, for example at very short periods of 2-3 ms. A time slot is placed in the part of the half cycle where current flows across the transformer and where the influence of harmonics is the smallest. Finding the part of the time slot could be done empirically at the installation stage of a system using the present invention, and it would thus be valid for that specific system. The signaling for communication with the LMS/SIU modules is generated via very short interruptions of the secondary side transformer circuit, whereby a high impedance occurs, and thus a pulse of high voltage is generated on the primary side of the transformer at each interruption in the assigned time slot TS. Thus, the interruptions generate high frequency pulses superimposed on the mains frequency in the allocated time slot TS, with clear discrimination against distortions when detected by the SCM unit 60. The series circuit 30 controlled by the control circuit 32 switches during very short intervals, thereby generating a controlled high impedance on the secondary transformer side. The present invention always involves the application of a controlled high impedance for communication pulses contained in the pulse signals. It generates a voltage pulse during a short time of the mains frequency half cycle. The totality of such pulses generated during a specific half cycle are transmitted as a pulse signal on the series cable.

According to the present invention, existing current transformers and not additional transmitters are used to supply a load and to generate high frequency pulse signals, wherein a pulse signal contains a number of pulses, and wherein each individual pulse is generated by a pulse-like influence on the impedance during a short time (generation of a high impedance) compared to a half cycle in which a current flows. The interruption of the secondary side circuit is therefore so short that the influence on the energy supplied to a load is negligible.

If interruptions on the secondary transformer side are, for example, longer than a line frequency half cycle, the transformer will saturate, resulting in almost no impedance, i.e. no generation of a high voltage pulse, but a hard-to-detect distortion due to the change in magnetic flux. In the context of the prior art, a transmitter connected to the series cable via a specially designed transformer would be required to generate a high voltage pulse according to the present invention.

The receiver located in the SCM unit for signals from the LMS and/or SIU modules is only disconnected during those time slots during which a transmission is in progress. This implies that transmitter and receiver should be synchronized in time and the accuracy should be in the range of 0.1 ms. For the skilled person it would have been natural to use zero crossings for synchronizing the time slots with the mains frequency. Unfortunately such an approach has disadvantages regarding additional zero crossings due to the harmonics with superimposed noise. To overcome Such disadvantages, according to the present invention, an embodiment of an inventive solution for synchronizing a time slot with the half cycles is disclosed.

Referring to Fig. 6, it is shown that a preferred solution is based on a method for determining the center of gravity for that specific time tc of the mains frequency where the area under the curve for the half cycle is equal on both sides of tc, i.e. the area to the left of tc is expressed as Y1, and is equal to the area to the right of the time tc, expressed as Y2. It is to be noted that the area around tc is not symmetrical due to the modulation of the current from the current generator. Both the transmitters and the receivers are required to calculate the position of the center of gravity and thereby position the time slot for communication in relation to the time tc.

The circuit according to Fig. 7 represents an inventive circuit design for synchronizing the time slots in relation to the time tc for an assumed center of gravity according to Fig. 6.

There are other possible embodiments with regard to synchronization within the scope of the present invention for a person skilled in the art, including software solutions. Further solutions for synchronization between an SCM unit 14 and LMS/SIU modules could be, for example, filtering each half-cycle signal - for example with a suitable bandpass filter - and applying the time when, for example, half of the peak value is retrieved, possibly in combination with a phase-locked loop technique. It is also within the scope of the present invention to claim such a solution for a message transfer system in connection with lighting systems, in particular for systems for airfields.

Referring to Fig. 6 and Fig. 7, Fig. 7 shows a circuit 79 for generating a square wave C0 whose frequency is twice the mains frequency and whose phase is designed so that its negative edge coincides with the center of gravity at time tc. An operational amplifier A1 is connected as an inverter A1. A2 and A3 are amplifiers connected as integrators (12, 13). 51, 52 and 53 are semiconductor switches. FF is a flip-flop used as a frequency divider and VCO is a voltage controlled oscillator. When C3 is at a high level, 51 leads and the integrator A2 integrates the range Y1 and C2 is at a high level. level, 52 conducts, and A2 integrates the range Y2, but with an opposite sign, so that the output voltage of A2 at the negative edge of C2 is proportional to Y2-Y1. During the time that C2 is high, 53 is conducting, and if the output voltage of A2 is separated from zero, the output voltage of A3 increases or decreases, depending on the polarity of the A2 output voltage. Accordingly, the VCO increases or decreases its output frequency. An output voltage of A3 remains constant if the C0 frequency is equal to twice the mains frequency, and the phase for C0 is such that Y1 = Y2. The feedback of the signals C2, C3, C4 is achieved via a gate circuit G.

Further reference is made to Fig. 6 and Fig. 7. In general, any device for synchronizing pulse signals to modulated AC line frequency half cycles may be used by performing the following procedure for determining the time tc which establishes the center of gravity for an AC half cycle amplitude signal. The device should have means 79 for determining a time tc for which the range Y1 before the time tc is equal to the range Y2 after the time tc. The determination of the time tc is carried out with reference to a suitably preset time at the start of a repeated cycle for determining the time tc.

Furthermore, the device should have means 79 for continuously synchronizing the pulse signals to modulated AC mains frequency half cycles to determine a time tc for which the amplitude signal range Y1 before the time tG is equal to the amplitude signal range Y2 following the time tG. The means 79 should include first means 12 for integrating the half cycle signal amplitude ranges Y1, Y2 for the range Y1 during a preset time and for the range Y2 for the remaining half cycle time following the preset time. The next action taken is to compare the integration results of the devices 11, 12 for comparing the ranges of the integrated amplitude signals, applying the output of the comparison to the control device 13 for controlling the preset time to obtain an offset by means of FF, G. The offset induces a control at the time tc. The integration is repeated until the ranges Y1, Y2 are equal to find the time tc and apply it as a reference for synchronizing the pulse signals.

A preferred starting value for the preset time period could be the time corresponding to ¹/₄ of the cycle time of a non-modulated sinusoidal AC mains frequency signal, i.e. 5 ms for 50 Hz and approximately 4.17 ms for 60 Hz.

A device as described above could be used in the main control system of an airport lighting system, connected to a serial cable, for time slot synchronization to AC mains frequency half cycles.

It is preferably correct to assume that a part around or adjacent to a centroid for a modulated AC line frequency half-cycle amplitude signal contains less distortion than other parts, for example, parts near a zero crossing of a modulated signal.

The coding of the communication signals is based on synchronization with the mains frequency and a specific procedure for inserting the time slots, where each half cycle of the mains frequency contains a time slot. The message transfer or communication is carried out according to a master/slave principle, where an SCM is the master and the distributed LMS/SIU modules are slave units. An SCM sends instructions, addressing the LMS and/or SIU module group concerned, and the LMS/SIU modules respond with their status information (ON or OFF) in sequence, every single half cycle in a time slot. The SCM sends messages (SCM messages) at programmable (i.e., in terms of the number of time slots) time intervals, for example one message every 30th half cycle. A message could contain, among other things, a message number, an instruction, and an address to the specific LMS group for which the message is intended. Each one of the 30 time slots after the SCM message has a time slot number determined by the SCM message number and the specific sequence number for the time slot, i.e. its position after the SCM message. In these specific embodiments, a maximum of 30 LMS units are able to respond to an SCM message, after which a new SCM message is sent.

In connection with the installation of the reporting and monitoring method and system according to the present invention, each LMS/SIU module is assigned one or more group addresses, as well as one or more time slots during which the LMS(SIU modules should respond with their status information, for example ON, OFF or ERROR.

This means that SIU modules with a requirement for a fast response - for example, sensors equipped with SIU modules - are allocated at least one time slot for each SCM message number, so that other LMS modules are allocated a time slot that only corresponds to a specific SCM message number. As mentioned, the SCM message is transmitted according to uniform or even-numbered time intervals, but the message number can be chosen so that the subsequent time slots contain responses from the LMS/SIU modules that must respond at the given time. For example, if an instruction is sent and addressed to a specific group, a response for that group is expected as soon as possible as receipt of the instruction and its acceptance. The message transmission sequences are described in more detail below.

Referring now to Fig. 8, a series circuit 2 with its connectors and interfaces according to the invention is shown. The light monitoring circuit system is designed for use in an airfield lighting control system and can be integrated into existing series circuits. A small electronic module LMS and/or SIU module (designated SIU in Fig. 8) is attached to each load 4, 9 which is to be individually monitored and/or switched on/off. High frequency signals superimposed on the power line network are used for communication between units. Accordingly, no additional cabling is required in the field.

In this preferred embodiment, the system is specified for series circuits operating in a current range of approximately 2.8-6.6 A and voltages up to 5 kV.

The LMS/SIU module is an individually addressable module, and each module has its own set of parameters for defining its working area, including its unique identity. Parameters are described and listed below.

The SCM unit transmits communication signals to and from the series connections of modules such as LMS 10/DIU 11. It receives and transmits data blocks from or to a CU unit 24, for example via an RS-232- C serial communication cable 2.

Accordingly, the CU 16 distributes and collects information to and from a number of SCM units 60 depending on the system complexity. The CU 16 itself communicates either with another CU 16 or another Unit such as a personal computer (PC) 24, 25 or other central processor-based units depending on the system complexity.

A series circuit filter (SCF) 62 prevents high frequency communication signals from reaching the CCR unit 12 of the circuit.

Transformers 6 are, for example, of the type Isolation transformer FAA 830, 200 W. The LMS, SCF and SCM connectors 96 are, for example, of the type L-823. Furthermore, the SCF connection 98 is achieved with T-adapters via the CCR output.

Fig. 9 shows an Airfield Smart Part ® (ASP) controlled airfield lighting system.

Each assembly of lights to be operated as a group, separate from other assemblies, is assigned an alpha-numeric "light function designation" TWY1, TWY2, TWY3, L01, SB1 etc. Examples of such assemblies are stopbars (SB), guide lines (LO) and taxiway (TWY) segments in a taxiway guidance system. In this embodiment, each light can form part of up to four function assemblies. Fig. 9 shows a light connected to three light functions (G1,2,3).

A lighting function setup can consist of lights connected to different series circuits. All lights connected to a series circuit belonging to the same lighting function are assigned a group address (G1, G2, G3, G4, G5) that is unique to this lighting function for this specific circuit.

All lights are assigned an individual address (A1, A2,.., A7, A8) that is unique to the circuit to which the light is attached. So-called light fixtures with two separately controlled lamps are assigned an address for each lamp.

Sensors in an ASP controlled airport lighting system are designed as follows.

Each assembly of sensors that are to be operated as a group, generally a transmitter and a receiver, is assigned an alpha-numeric "Sensor Function" designation.

A sensor 9 may have one or more inputs for self-testing etc. Each sensor 9 input (maximum four in this embodiment) is assigned a group address which is unique to the series circuit to which the sensor is attached. The sensor is attached via a sensor interface unit (SIU) which is connected to the series circuit via an isolation transformer 4 and the communicates with the SCM 60 in the same way as the LMS/SIU modules 10, 11.

All sensors are assigned an individual address that is unique to the circuit to which their receiver is connected. In this embodiment, each receiver can have up to three inputs and up to four outputs that can be controlled with the address.

Information exchange is carried out according to the structure shown in Fig. 10, and the arrows show the exchange flow. The top box in the figure represents the higher system level.

Communication between different levels is of the master/slave type, where the higher level is always the master. The master causes a call to the slave units, evaluating the response, and if a specific program condition is met, the polling sequence is interrupted and an instruction is sent down to the system, whereby the evaluation of entered or specified conditions is carried out at the system level that is as low as possible. To achieve short response times, the information is condensed as much as possible before being transmitted up to the system. Thus, the requirements for the channel for transmitting the information can be kept at a low level. Generally, only information related to changes in status is transferred from one level to another. For example, information about the status of individual lights is only sent up in the system when a lamp fault occurs. As long as the lamp is working, its status can be evaluated based on the status of the lighting functions to which it belongs.

A protocol used for interfacing communication with an external host system can be of a standard type, such as Allen-Bradley Data Highway + or Omron Sysway System. The protocols used for communication between CU and SCM and between LMS Modules 10 or SIU Modules 10 are proprietary. Depending on the application, RS-232, RS-485, short-range modem or fiber optic modem can be selected.

With regard to communication between LMS/SIU modules and SCM units 60, signals are synchronized with the line frequency such that one bit is sent every half cycle, and each bit consists of a burst of pulses. The frequencies of these preferred embodiments are chosen, for example, in the range 4-7 kHz as follows:

From SCM: "1" = f1 (frequency 1)

"0" = f3 (frequency 3)

From LMS "1" = f2 (frequency 2)

"Q" = f3 (frequency 3)

SCM 60 often sends synchronization signals according to one of the methods described below, with or without instructions, to the LMS and/or SIU modules. The LMS and/or SIU modules respond, one at a time, during the time slot (half cycle) given by an individual address for an LMS or SIU. According to this procedure, the LMS or SIU modules respond with a "1" when a load is ON and with a "0" when it is OFF. In the case of a load 4, 9, an error non-response signal is transmitted.

There are two types of synchronization signals: the "Shortsync" (SS) and the "Longsync" (LS). When no instructions are being transmitted, an SS is transmitted repeatedly for LMS/SIU module monitoring purposes. An LS contains an instruction that is transmitted only when a new command is to be executed and is repeated until satisfactory responses are received from the LMS/SIU module. The SS and LS are both numbered #1 to #8 in this embodiment, but are preferably programmable.

Referring now to Fig. 11, an illustration of the shortsync procedure is given. The time between shortsync units is given by the number of occupied time slots between synchronization words (sync words). It is preferred that each LMS or SIU module can be assigned two time slots following each other out of the eight possible sync words, but generally only one time slot follows one of the eight sync words assigned to an LMS.

Considering a sensor 9 as a load, a SIU is generally assigned a time slot after each of the eight sync words. Fig. 11 shows an example where a total of 240 time slots are used for communication, corresponding to an airfield lighting system with, for example, 240 LMS modules or 160 LMS modules and 10 SIU modules. The time period for a mains frequency of 60/50 Hz with respect to one sync word and 30 time slots is 304 or 380 ms, and the total for eight sync words and 240 time slots is 2432 or 3040 ms, respectively. As mentioned, sync words are transmitted and time slots are assigned repeatedly. Accordingly, sync word #1 is sent after a time slot 240 has elapsed, and the procedure is cyclically repeated. repeated in a stationary sequence, unless interrupted by a long sync.

Refer again to Fig. 11 for an explanation of the fields of the Shortsync unit, and these are Startbit, Number, Identifier and Checksum (Startbit, No, Id, CRC). The Shortsync unit contains 8 bits, 1 bit for the start bit, 3 bits for the number (nnn), 1 bit for Id and 3 bits for the checksum (ccc). The start bit "1" corresponds to a frequency that is only used by the SCM units and not by the LMS and/or SIU modules. The three number bits nnn decide from which LMS a response is requested and the ID field corresponds to [0 = Shortsync]. To minimize the risk of false detection due to distances, a checksum (ccc) according to a cyclic redundant code (CRC) is added. CRC codes are well known in the art, and therefore a detailed description of the technique is omitted here.

Reference is made to Fig. 12 for the transmission of LS. When there is an instruction to be transmitted, the stationary sequence is interrupted, except that completion of the last transmitted short sync number sequence is allowed, e.g. sequence #7 if applicable. Thereafter, the long sync word is transmitted with the appropriate command, choosing the sync number (sync #) to correspond to the time at which the addressed group has a time slot within which to respond.

Fig. 12 is an explanation of the fields in LS, and these are Startbit, Number, Identifier, Checksum, Group Number, Instruction and Checksum [Startbit, No, Id, CRC1, Groupadr, Order, CRC2j. The LS contains 23 bits, one bit for the start bit, 3 bits for the number (nnn), one bit for Id and 3 bits for the checksum (ccc). The three number bits nnn determine from which LMS and/or SIU a response is requested and the ID field corresponds to [1 = Longsync]. To ensure an initial checksum (ccc) a CRC code is added to detect errors in the number and/or ID fields. The group address contains 7 bits (gggggggg) to address the command to the intended group address. The next field contains the specific instruction over four bits (zzzz). For example, an instruction can be of type (0000) which means turning the lamp on, (0001) turning the lamp off, (0010) flashing the lamp on, etc. The last 4 bits in the second CRC field are determined and calculated using a polynomial with the reference symbol CRC-BCH = x⁴ + x + 1.

The LMS and/or SIU modules have their own groups of parameters, defined by two blocks. Block 1 contains the parameters Time Slots and Group Addr, and they are downloaded during initialization or a change in system configuration. The Time Slotting procedure was covered above. The Group Addr defines which group sequence to respond to. Since an LMS can be part of several groups, up to four group addresses (A-D) can be defined in this embodiment. In practice this means that an LMS with its group address set to, for example, (10, 64, 0, 0,) will respond to instructions received when the group address for the instruction is 10 or 64.

A second block (block 2) of this embodiment contains for example, the following parameters:

Target Group Address - Parameter Block 2 is downloaded to all LMS and/or SIU modules that have one of their group addresses set to a number according to the Target Group Address in Parameter Block 2; Default - Default status (on = 1/off = 0) for the LMS and/or SIU modules when the series connection is powered up;

Inverse function - states that the LMS should assume, as opposed to an on/off instruction, to switch the lamp on when the instruction is off and vice versa (no inverse function = 0, inverse function = 1);

Backup Status - If communication is interrupted for a time longer than the time specified by the Timeout parameter below, the LMS and/or the SIU will switch the lamp to On = 1, Off = 0 or No Change = 2 according to this setting;

Min ALC f~ - Minimum signal level for detecting the received data "0"; and

Min ALC fa - Minimum signal level for detecting the received data "1"

A stationary sequence is given by Shortsynch1, Shortsync #2, ..., Shortsynch8, Shortsynch1, Shortsynch2, ... etc. The time between Shortsync units is given by the number of occupied time slots between the sync words. Time slot 1 is represented by the first half-network cycle after the Shortsync. A possible modification of the stationary sequence is that if there is a missing response from a responsible LMS, the same Shortsynch can be repeated. If the response from the LMS is still not available after the repetition, it is assumed that there is an error for the connected lamp (load).

If a sequence of instructions is to be transmitted, the stationary sequence is interrupted, with the exception that at least the last short sync sequence can be completed and a long sync word with an appropriate command is sent. The sync is chosen so that responses from the addressed groups are received immediately after the long sync. One possibility is to repeat the same long sync words, unless LMS or SIU modules in the addressed group respond with a correctly changed status.

If the LMS and/or SIU has received a download command, the checksum is checked. In the case of a parameter block 1, it is also checked whether a lamp or load is disconnected. If this is the case and a long sync word is received after the parameter block (as a communication check), the new parameters are stored in the LMS or SIU modules EEPROM. Otherwise, the modules are reset and the previously used parameters are used. If two short syncs are received before a long sync, the LMS or SIU is also reset.

During a reset operation, the parameters stored in the EEPROM are loaded into a working memory, and a checksum is calculated and compared with the checksum stored in the EEPROM. Then, if a checksum error is detected, the lamp is turned off, slot addresses and group addresses are removed, and the other parameters are set to the default values as specified.

The checksum is calculated for parameter block 2 plus group addresses 1-4 using CRC/CCITT. This 2-byte checksum is stored in the EEPROM. The download parameters can be controlled using the "checksum question" and used to compare with the 2 bytes in the "checksum question" where the most significant bit in each byte is ignored.

While the foregoing description merely describes the embodiments of this invention as shown and/or described, it is to be understood that other embodiments may be articulated as well.

Accordingly, the terms and expressions used herein are for the purpose of describing the invention by way of example only and do not limit does not affect the invention. In particular, each of the specific construction elements described may be replaced by any other known element having an equivalent function.

Claims (32)

1. Method for the transmission of control and monitoring information between a main controller (14, 16, 24) and at least one addressable light monitoring switching module (10) or a sensor interface unit module (11), wherein each light monitoring switching module (10) and sensor interface unit module (11) is connected to the secondary side of each dedicated isolation transformer (6), the primary side of which is connected in series to a power cable (2) to which an AC mains frequency current is supplied by a constant current generator (12), with a filter (62) connected to prevent high frequency signals from reaching the constant current generator, and the transfer signals are superimposed on the AC mains frequency current, to achieve control and monitoring of the loads (4, 9) in airport lighting systems, wherein a portion of the AC mains frequency half-cycle time slots for the message transfer are superimposed with superimposed high-frequency high-voltage pulses as carriers of the data in each time slot, the pulses on the primary transformer side occur through short interruptions of a series circuit (30) controlled by a control switch (32) on the secondary side, and the interruptions generate a controlled high impedance, whereby the interruptions occur in the time slot, wherein in the total number of interruptions each generates a high voltage pulse on the primary transformer side to form a pulse signal for transmitting the data, the transfer enables control of the load functions and the nature of the loads’ status, and the time slots are synchronized with the part of the AC mains frequency current that is determined to contain almost no or little distortion compared with the pulse signals. 2. Method according to claim 1, characterized in that a pulse signal carries a digital data bit in each time slot, whereby the pulse signal contains a bundle of high voltage pulses superimposed on the AC mains frequency half cycles. 3. Method according to claim 1 or 2, characterized by determining the center of gravity of the AC mains frequency half cycles and using it as a reference for synchronizing the time slots via the determination of a time (tc) at which the mains frequency signal amplitude range on both sides of the mains frequency half cycle is equal on the sides. 4. Method according to claim 3, characterized in that the determination of the time (tc) is carried out by integrating the areas (Y1, Y2) individually, by comparing the areas, by determining the offset and by repeatedly integrating until they are aligned with each other. 5. Method according to one of the preceding claims, characterized in that all loads (4, 9) connected to the series circuit are assigned an individual address which is unique for the circuit to which the load is attached. 6. Method according to claim 5, characterized in that on lighting fixtures with separately controlled lamps, an address is assigned for each lighting fixture lamp. 7. Method according to claim 5 and 6, characterized in that each structure of loads that are to be operated as a group is provided with an alphanumeric load function designation (TWY1, LO1, SB1) separately from other structures. 8. Method according to claim 7, characterized in that each light monitoring switching module (10) and sensor interface module (11) is assigned one or more group addresses, the group addresses each belonging to a specific load function. 9. Method according to claim 8, characterized in that the modules are assigned one or more time slots (TS) during which they should respond with their status information. 10. Method according to one of the preceding claims, characterized in that the sequences for establishing a transmission of monitoring and control information along both directions on serial cables between communication units are formed by cyclically transmitting a number of synchronization signals of a first and a second type from the main controller (14), each number being programmable, and each of the synchronization signals being followed by a programmable number of time slots (TS). 11. Method according to claim 10, characterized in that the first type of synchronization signal triggers a sequence that is used for monitoring purposes and that the second type of synchronization signal triggers a sequence in which commands are to be transmitted. 12. Method according to claim 11, characterized in that the second type of synchronization signal has priority over the first type of synchronization signal and can therefore interrupt the first type of synchronization signal sequence when commands are to be transmitted. 13. Method according to claim 12, characterized in that time slots following the first synchronization signal can be terminated. 14. A method according to claim 13, characterized in that the second synchronization signal is selected so that responses from the addressed groups are obtained immediately after the second synchronization signal. 15. Method according to claims 9 to 14, characterized in that in the event of a missing response from a previously responding light monitoring switching module (10) or a sensor interface module (11), the same synchronization signal is repeated in the programmable number of times, and if there is still no response, it is assumed that there is an error in the load. 16. System adapted for the transfer of control and monitoring information between a main controller (14, 16, 24) and at least one addressable light monitoring switching module (10) or sensor interface module (11), wherein each light monitoring switching module (10) and sensor interface module (11) is connected to the secondary side of each series isolation transformer (16), the primary side of which is connected in series to a power cable (12) to which an AC mains frequency current is supplied by a constant current generator (12), with a filter (62) connected to prevent high frequency signals from reaching the constant current generator, and the transfer of a signal is superimposed on the AC mains frequency current for achieving control and monitoring of loads (4, 9) in airport lighting systems, wherein a part of the AC mains frequency half cycles forms time slots for a message transfer with superimposed high-frequency high-voltage pulses, which are carriers of data in each time slot, the pulses occur on the primary transformer side through short interruptions of a series circuit (30) - controlled by a control switch (32) on the secondary transformer side - whereby the interruptions generate a controlled high impedance, whereby the interruptions occur in the time slot, whereby the totality of the interruptions each generates a high voltage pulse on the primary transformer side, for forming a pulse signal for transferring the data, whereby a main controller (14, 16, 24) is adapted to use the transfer of data for controlling load functions and for reading the status of the loads, a series connection modem (60) connected to the series isolation transformer (16) is adapted to synchronize the time slots to the portion of the AC mains frequency current determined to have almost no or little distortion compared to the pulse signals, whereby the high voltage pulses are generated by existing series isolation transformers (6) by the light monitoring switching module (10) and the sensor interface unit module (11). 17. A system according to claim 16, characterized in that a pulse signal carries one digital data bit in each time slot, whereby the pulse signal contains a burst of high voltage pulses superimposed on AC mains frequency half cycles. 18. System according to claim 16 and 17, characterized by a device (79) adapted to determine the center of gravity of the AC mains frequency half cycles and to use these as a reference for synchronizing the time slots by determining a time (tc) for which the mains frequency signal amplitude range on both sides of the mains frequency half cycle is equal on both sides. 19. System according to claim 18, characterized in that the device (97) is adapted to determine the time (tc) by integrating the ranges (Y1, Y2) individually, as well as to compare the ranges, determine the offset and repeatedly integrate until they are matched with each other. 20. System according to claim 16 to 19, characterized in that all loads (4, 9) connected to the series circuit use an individual address that is unique to the circuit to which the load is to be attached. 21. A system according to claim 20, characterized in that lighting fixtures with separately controlled lamps use an address for each lighting fixture lamp. 22. System according to claim 20 and 21, characterized in that each structure of the loads to be operated as a group, separate from other structures, uses an alphanumeric load function designation (TWY1, LO1, SBl). 23. System according to claim 22, characterized in that each light monitoring switching module (10) and sensor interface module (11) is assigned one or more group addresses, each of which belongs to a specific load function. 24. System according to claim 23, characterized in that the modules are assigned one or more time slots (TS) during which they should respond with their status information. 25. System according to claims 16 to 24, characterized in that the sequences for establishing a transmission of monitoring and control information along both directions on serial cables between the communication units are formed by cyclically transmitting a number of synchronization signals of a first and a second type from the main controller (14), each number being programmable, and each of the synchronization signals being followed by a programmable number of time slots (TS). 26. System according to claim 25, characterized in that the first type of synchronization signals triggers a sequence used for monitoring purposes and that the second type of synchronization signals triggers a sequence in which commands are to be transmitted. 27. System according to claim 26, characterized in that the second type of synchronization signal has priority over the first type of synchronization signal and can therefore interrupt the first synchronization signal sequence when commands are to be transmitted. 28. System according to claim 27, characterized in that time slots following the first synchronization signal can be terminated. 29. A system according to claim 28, characterized in that the second synchronization signal is selected so that responses from addressed groups are obtained immediately after the second synchronization signal. 30. System according to claims 24 to 29, characterized in that in the event of a missing response from a previously responding light monitoring switching module (10) or sensor interface module (11), the same synchronization signal is repeated in the programmable number of times, and if there is still no response, a fault in the load is assumed. 31. System according to claim 18, characterized in that the device (79) for determining a time (tc) includes a first device (12) for integrating the half-cycle signal amplitude ranges (Y1, Y2) for the range (Y1) during a preset time and for the range (Y2) for the remaining half-cycle time after the preset time, comparing the integration results with a device (11, 12) for comparing the ranges of the integrated amplitude signals, further applying the output from the comparison to the control device (13) for controlling the preset time to be offset by a device (FF, G) for achieving an offset from the time (tc), repeating the integration until the ranges (Y1, Y2) are equal, finding the time (tc) and using it as a reference for synchronizing the time slots. 32. System according to claim 31, characterized in that the starting value for the preset times is the time for 1/4 of the cycle duration time of a non-modulated sinusoidal AC mains frequency signal, i.e. 5 ms for 50 Hz and approximately 4.17 ms for 60 Hz.